Another Zenith problem

[Allenk]

Ok I have a set a Zeniths. They are nice and tight at the shaft and I get adjustment at the mixture screws to the point where it will affect the idle. The problem is The engine seems to be getting fuel from somewhere other than the idle circuit. The idle speed screws are down at about 3/4 so I know I'm not blowing by that circuit and pulling from the high speed circuit. The carbs are rebuilt and I've tried running w/o and washers at the needle valves to run the bowl level at it's lowest but fuel just keeps coming. When I turn the engine off, I can here the fuel dripping into the exhaust. I've tried running the car as low as .5psi and the problem is still there. Could the pressure regulator be junk? Could it be a valve issue. The timing is right on at set at high speed. Any ideas? The floats seem fine, could the float linkage be bent? How can I tell?

[Allenk]

More info: I started taking the carbs apart and there is fuel in the top area of the carb so fuel is either blowing by the needles or coming through the emulsion tubes( from too high of a fuel level in bowl?). Is anyone else running Zeniths w/o a return to the tank? Is this my proble? Having continuouse running fuel pump?

[oldE]

If the problem started after the rebuild, I would guess the floats are not doing their job. Check the float valves.
Les

[Allenk]

They are new so I'm not sure what to check. I have put air to them and they seem to hold back.

[project 911]

Allenk-

What pump and reg are you using?
I just went through big issues with fuel pressure/volume and Zeniths.

[Allenk]

The pump is of unknown name and origin since it and the reg where in the car. The Regulator is a purolator that I've seem in a lot of porsche catalogs-somewhat inexpensive.

[A Quiet Boom]

Get a gauge on there and check actual pressure. I've had a lot of carbs do what your's are doing because the pressure was to high.

[project 911]

Allenk-

The only thing I know of that will spill fuel out your vent tubes is stuck needles, or pressure so high that it is blowing by them. Not sure if this is true of Zenith, but I've heard that 6+ pounds will blow them.
I had a new regulator that was probably like your Purolator (dial on top), and it showed 3-4 pounds on the guage, but I found that the volume going through it was almost nothing. Not your problem, but these regs can go bad. You may be getting full pressure though it that is causing your problem. I've also had gauges (new) that weren't true.
I picked up a Holley reg that is working great, and solved many of my troubles. Less than $30.

The float linkage is pretty sturdy, so I doubt it is bent, but check to make sure the screws that hold the float assembly to the upper housing are tight. I've seen them work loose. My vote is the fuel regulator.

Good luck-

[Allenk]

I'm in agreement w/ starting at the regulator. I checked flow last night and the regulator I have does restrict the flow quite a bit. I also don't think that is the problem but it probably isn't accurate for pressure either.

[project 911]

It would be good to know if you have a pump made for carbs, or if it was for fuel injection (much higher pressure). Was the car converted to carbs? Might be good to check the pressure and flow before the regulator too. My original pump had a return line and works with an internal check valve that would send over-pressure back to the tank. These check valve can stick and cause trouble. I think they have rebuild kits for that (?). Have you tried putting your old needle valves back in to see what happens?
Keep at it...

[Allenk]

The bad thing is I have no idea what the pump is. I'm wondering about the whole check valve/return line situation. My pump does not provide for a return line. I put the old needle valves back in last night and thought they made a difference but at that point I'd been sucking on so much fuel filled exhaust I couldn't be sure of anything. The car is a 71T that came with Zeniths but someone along the way put an aftermarket pump in.

[mb911]

I have zeniths on my 2.7 with no return. There is a little fuel on top (emulsion tubes) but not to much and I also do not have a return. I run a fuel pump that produces about 3-4 psi (have an extra if you want to try it) I have never had problems with it dripping fuel into the combustion chamber. I would vote the needles are not holding back the pressure. I also think a little bit of fuel on top is probably fine as the this is were fuel and aire mix for the air correction jets.

Ben

[Allenk]

I guess I would really like to take you up on trying a different pump mb911. I really want to get this solved.

[mb911]

Are you really in Wisconsin? As your location indicates? Give me your shipping address and we can figure it out

Ben

[Allenk]

I am. Check your PM

[mb911]

I checked PM and nothing You can run over and pick it up as I am about 20 minutes from paddock lake

Ben

[Chrisrad99]

I had a problem with too much fuel pressure on zeniths. Fuel leaked from the overflow tubes initially, however after a few minutes there was no fuel pressure at all.

It turned out to be a clogged return line from the fuel pump to the gas tank. Your 71 should have a return line.

[Allenk]

I was wondering how successful people were running w/o the return. Mine has always been disconected since I bought the car. Then again, it didn't run either. Now I'm running strong without popping at all but I rich as all get out at idle.

[project 911]

Allenk-

I'm running a vintage AC pump up front (about 10psi) with a Holley regulator back near the carbs. No return line, and it seems to be working fine. It may depend on your pump. If it is working to hard on the deadhead system, you may want a return line to keep your pump running cooler.
I was planning to use one, but since the regulator needs to be in the back near the carbs, I didn't want to deal with plumbing a new return line from the back to the front.

[Allenk]

I have the line that runs through the tunnel but my pump doesnot provide for a return line. How would one get plumb in?